The principal investigator has access to, or has raised himself, antibodies against smooth muscle myosins, alpha-actinin, tropomyosin, and actin. The antibodies will be labelled with either rhodamine or fluorescein and used with isolated smooth muscle cells or myofibrils in "double-labelling" experiments to ascertain: 1) whether actin and myosin are segregated into complementary bands in smooth muscle myofibrils. 2) whether tropomyosin is found in the same locations as actin in smooth muscle myofibrils. 3) whether alpha-actinin is part of an extra-myofibrillar cytoskeleton. 4) whether Z-lines or their equivalent exist in smooth muscles. 5) the organization of attachment sites for myofibrils. Complementary work with the one-million volt electron microscope at Oak Ridge National Laboratories will also be carried out.